Filtration media and applications thereof

ABSTRACT

In some embodiments, the present invention provide filtration media for the treatment of flue gas streams and methods of making and using the same. In one embodiment, a filtration medium comprises a pollutant absorbent layer comprising a plurality of activated carbon fibers, at least one woven fabric, and at least one non-woven fabric, wherein the pollutant absorbent layer is positioned between the at least one woven fabric and the at least one non-woven fabric.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/364,197, filed on Jul. 14, 2010, the entire disclosure of which is hereby incorporated by reference

FIELD OF THE INVENTION

The present invention relates to filtration media and, in particular, to filtration media used in flue gas applications.

BACKGROUND

The hazards of nitrogen oxides, mercury and other compounds present in flue gases have resulted in the imposition of strict standards limiting discharges of such chemical species. To meet these standards, it is necessary to remove a significant portion of nitrogen oxides, mercury and/or other chemical species present in exhaust gases from stationary or mobile combustion sources.

Denitrification or selective catalytic reduction (SCR) technology is commonly applied to combustion-derived flue gases for the removal of nitrogen oxides when passed through a catalytic reactor. SCR technology has progressed to where substantially all nitrogen oxides can be removed from a flue gas.

Effective and efficient removal of mercury from flue gases, however, has become increasingly difficult. Elemental mercury in flue gases does not adhere well to soot and/or other particulates making collection by conventional particulate collection methods, such as electrostatic precipitators, dust filters and scrubbers, difficult. Moreover, the environmentally demanding and destructive conditions associated with flue gas filtration and treatment render many mercury absorbing materials unsuitable for use in industrial processes such as pulse jet or reverse air applications.

SUMMARY

In one aspect, the present invention provides filtration media. In some embodiments, filtration media described herein are operable to remove one or more pollutants from a flue gas stream including, but not limited to, mercury and/or heavy metals. Filtration media described herein, in some embodiments, are suitable for use in pulse jet and/or reverse air processes.

In some embodiments, a filtration medium comprises a pollutant absorbent layer comprising a plurality of activated carbon fibers, at least one woven fabric; and at least one non-woven fabric, and wherein the pollutant absorbent layer is positioned between the at least one woven fabric and the at least one non-woven fabric.

In some embodiments, the pollutant absorbent layer is needled to the at least one woven fabric and the at least one non-woven fabric. In some embodiments, the filtration medium further comprises a second non-woven fabric. In some embodiments, the second non-woven fabric is positioned on an opposite side of the pollutant absorbent layer from the at least one non-woven fabric. In some embodiments, the first non-woven fabric, the pollutant absorbent layer, the woven fabric, and the second non-woven fabric are needled together.

In some embodiments, the at least one woven fabric and the at least one non-woven fabric comprise glass fibers, synthetic polymeric fibers, inorganic fibers, natural fibers, or combinations thereof In some embodiments, the at least one woven fabric and the at least one nonwoven fabric comprise E-glass fibers, C-glass fibers, ECR glass fibers, S-glass fibers, zero-boron glass fibers or mixtures thereof

In some embodiments, the at least one non-woven fabric has a thickness up to about 0.2 inches. In some embodiments, the at least one non-woven fabric has a permeability of at least about 80 scfm/ft² according to ASTM D737. The at least one woven fabric, in some embodiments, has a thickness up to about 0.2 inches. In some embodiments, the at least one woven fabric has a weight of less than about 25 oz/yd². The at least one woven fabric has a weight of at least about 1 oz/yd² in some embodiments. In some embodiments, the at least one woven fabric has a permeability of at least about 100 scfm/ft² as measured according to ASTM D737.

In some embodiments, the activated carbon fibers comprise synthetic polymeric fibers, natural fibers, or combinations thereof. Synthetic polymeric fibers, in some embodiments, can comprise polyacrylonitrile fibers, phenolic fibers, polyvinyl alcohol fibers, or combinations thereof. The natural fibers, in some embodiments, can comprise cellulosic fibers or rayon precursors. In some embodiments, the activated carbon fibers are partially carbonized.

In some embodiments, the pollutant absorbent layer further comprises metal halide salts, metal hydroxides, inorganic acids, noble metals, or combinations thereof.

In some embodiments, the metal halide salt comprises zinc chloride, zinc bromide, or combinations thereof. In some embodiments comprising metal halide salts wherein the metal halide salt comprises zinc chloride, the zinc chloride can be present in amount ranging from about 0.25 to about 6 weight percent zinc. In embodiments comprising metal halide salts, the metal halide salts can comprise potassium chloride, potassium bromide, potassium iodide, or combinations thereof.

In some embodiments, the activated carbon fibers can have an average diameter of up to about 50 μm. The activated carbon fibers can have an average diameter of at least about 100 nm in some embodiments.

In some embodiments, the activated carbon fibers further comprise at least one mercury retention species. In some embodiments, the at least one mercury retention species comprises sulfur or a halogen. In some embodiments, the halogen comprises iodine, bromine, or chlorine. In one embodiment, the halogen comprises bromine. The halogen can be present in an amount of at least 1 weight percent in some embodiments. The halogen, in some embodiments, can be present in an amount of at least 5 weight percent.

In some embodiments, the pollutant absorbent layer has a surface area of at least about 150 m²/g as measured by ASTM D6556-10. The pollutant absorbent layer, in some embodiments, absorbs at least about 50 mg of mercury per gram of activated carbon fiber at room temperature in saturated mercury vapor. In some embodiments, the pollutant absorbent layer absorbs at least about 100 mg of mercury per gram of activated carbon fiber at room temperature in saturated mercury vapor. In some embodiments, the pollutant absorbent layer has a permeability of at least about 20 scfm/ft² according to ASTM D737.

The pollutant absorbent layer has a thickness of at least about 0.01 inches in some embodiments. In some embodiments, the pollutant absorbent layer has a basis weight of at least about 1 g/ft². In some embodiments, the pollutant absorbent layer has a basis weight of up to about 60 g/ft².

The filtration media of the present invention typically comprise a fluid inlet surface and a fluid outlet surface. In some of those embodiments, a coating can be provided on at least one of the fluid inlet surface and the fluid outlet surface. The coating can provide one or more functions depending on the coating selected and the desired characteristics. For example, and without limitation, various coatings can provide abrasion resistance, can assist in bonding of layers, can provide chemical resistance, and/or can provide non-stick properties. In some embodiments, the coating can comprise one or more of the following: at least one urethane, at least one silicone, at least one fluorocarbon, at least one epoxy, at least one silane, or at least one siloxane, or combinations thereof. In some embodiments where the coating comprises fluorocarbons, the fluorocarbon can comprise polytetrafluoroethylene.

In some embodiment, a membrane can be coupled to the at least non-woven fabric. The membrane can be a polytetrafluoroethylene membrane in some embodiments.

The filtration medium, in some embodiments, can have a thickness of at least about 0.1 inches. In some embodiment, the filtration medium can have a thickness of less than about 0.5 inches. In some embodiments, the filtration medium can have a permeability of at least about 10 scfm/ft² when measured according to ASTM D737. Some embodiments of filtration media can have a tensile strength of at least about 200 lbf/2 inches. In some embodiments, the filtration medium can have a MIT Flex count of at least about 300,000 relative to the width of the filtration medium.

In another aspect, the present invention relates to filtration systems including, for example, pulse jet flue gas filtration systems and reverse air flue gas filtration systems. In some embodiments, a filtration system can comprises a flue gas inlet manifold, a flue gas outlet manifold, and at least one filtration apparatus positioned between the flue gas inlet manifold and the flue gas outlet manifold, the at least one filtration apparatus comprising one of the filtration media disclosed herein disposed over a wire cage support.

In some embodiments, the filtration medium can be in the shape of a bag. In some embodiments, the at least one filtration apparatus can further comprise at least one support ring operatively coupled to the filtration medium.

In some embodiments, a filtration medium comprises a pollutant absorbent layer comprising a plurality of activated carbon fibers treated with a mercury retention species, at least one woven fiber glass fabric, and at least one non-woven fiber glass fabric, wherein the pollutant absorbent layer is positioned between the at least one woven fabric and the at least one non-woven fabric, and wherein the pollutant absorbent layer is needled to the at least one woven fabric and the at least one non-woven fabric. In some embodiments, a membrane can be coupled to the at least one non-woven fabric.

In another aspect, the present invention relates to methods of producing a filtration medium. In some embodiments, a method of producing a filtration medium comprises providing a pollutant absorbent layer comprising activated carbon fibers, positioning a non-woven fabric adjacent to a first surface of the pollutant absorbent layer, positioning a woven fabric adjacent to a second surface of the pollutant absorbent layer, and needling the at non-woven fabric and the woven fabric to the pollutant absorbent layer.

In some embodiments, such methods further comprise positioning a second non-woven fabric adjacent to the woven fabric prior to needling. In some such embodiments, the at least one woven fabric can be positioned between the second non-woven fabric and the pollutant absorbent layer. In other such embodiments, the second non-woven fabric can be positioned between the at least one woven fabric and the pollutant absorbent layer.

In some embodiments, a method of producing a filtration medium can further comprise applying a coating to at least one of a fluid inlet surface or a fluid outlet surface of the filtration medium.

Methods of producing a filtration medium, in some embodiments can further comprise attaching a fluorocarbon membrane to at least one of a fluid inlet surface or a fluid outlet surface of the filtration medium. In some embodiments, the fluorocarbon can comprise polytetrafluoroethylene.

In some embodiments, the methods can further comprise treating the pollutant absorbent layer with an aqueous solution comprising a metal halogen salt. The metal halogen salt, in some embodiments, can comprise zinc chloride, zinc bromide, potassium chloride, potassium bromide, potassium iodide, or combinations thereof. In some such embodiments, the treatment can comprise exposing a pollutant absorbent layer to the aqueous solution comprising a metal halogen salt and drying the pollutant absorbent layer. In some embodiments comprising a metal halogen salt, the metal halogen salt can comprise zinc chloride. In other embodiments, the metal halogen salt can comprise potassium bromide.

These and other embodiments are described in greater detail in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-sectional view of a filtration medium according to one embodiment of the present invention

FIG. 2 illustrates a cross-sectional view of a filtration medium according to one embodiment of the present invention.

FIG. 3 illustrates a cross-sectional view of a filtration medium according to one embodiment of the present invention.

FIG. 4 illustrates filtration apparatus of a pulse jet flue gas filtration system according to one embodiment of the present invention.

DETAILED DESCRIPTION

For the purposes of this specification, unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification are approximations that can vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Additionally, any reference referred to as being “incorporated herein” is to be understood as being incorporated in its entirety.

It is further noted that, as used in this specification, the singular forms “a,” “an,” and “the” include plural referents unless expressly and unequivocally limited to one referent.

In one aspect, the present invention provides filtration media that can be used, for example, in the treatment of flue gas streams. In some embodiments, filtration media described herein are operable to remove one or more pollutants from a flue gas stream including, but not limited to, mercury and/or other heavy metals.

A filtration medium, in some embodiments, comprises a pollutant absorbent layer comprising activated carbon fibers, a first non-woven fabric and at least one woven fabric, wherein the pollutant absorbent layer is positioned between and needled to the first non-woven fabric and the woven fabric. In some embodiments, the filtration medium comprises a coating on the fluid inlet surface and/or fluid outlet surface.

FIG. 1 illustrates a cross-section of a needled filtration medium according to one embodiment of the present invention. The filtration medium (100) illustrated in FIG. 1 comprises a pollutant absorbent layer (101) comprising activated carbon fibers positioned between and in contact with a first non-woven fabric (102) and a woven fabric (103). The surface (104) of the woven fabric (103) comprises a coating (105). While in FIG. 1, the coating (105) is appears to be a separate layer, it should be understood that the coating (105) is actually applied to the surfaces of at least a portion of the fibers in the woven fabric (103). In some embodiments, the coating (105) can inhibit degradation of the filtration medium (100) by enhancing the abrasion resistance of fibers protruding from the surface (104) of the woven fabric (103) resulting from needling the non-woven fabric (102), pollutant absorbent layer and non-woven fabric (102). In some embodiments, the coating (105) can be a non-stick or repellant to particles in the fluid stream, thereby facilitating cleaning of the filtration medium (100). In some embodiments, a membrane can be coupled (e.g., laminated) to the surface of the non-woven fabric (102). The membrane can be, for example, a thin polytetrafluoroethylene film in some embodiments.

In some embodiments, a filtration medium further comprises a second non-woven fabric spaced apart from the first non-woven fabric. The second non-woven fabric, in some embodiments, is spaced apart from the first non-woven fabric by the pollutant absorbent layer. In some embodiments, the second non-woven fabric is spaced apart from the first non-woven fabric by the pollutant absorbent layer and the woven fabric.

FIG. 2 illustrates a cross section of a needled filtration medium according to another embodiment of the present invention. The filtration medium (200) of FIG. 2 comprises a first non-woven fabric (201), a pollutant absorbent layer (202) comprising activated carbon fibers, a woven fabric (203) and a second non-woven fabric (204) needled together. The pollutant absorbent layer is positioned between the first non-woven fabric (201) and the woven fabric (203). The second non-woven fabric (204) is spaced apart from the first non-woven fabric (201) by the woven fabric (203) and the pollutant absorbent layer (202). The fluid inlet (205) and fluid outlet (206) surfaces of the filtration medium (200) comprise a coating which, in some embodiments, is operable to enhance the abrasion resistance of fibers protruding from the surfaces (205, 206) resulting from needling the filtration medium (200). In some embodiments, the coating is non-stick or repellant to particles in the fluid stream, thereby facilitating cleaning of the filtration medium (200) by techniques such as pulse jet or reverse air. In some embodiments, a membrane can be coupled (e.g., laminated) to the surface (205) of the non-woven fabric (201). The membrane can be, for example, a thin polytetrafluoroethylene film in some embodiments.

FIG. 3 illustrates a cross section of a needled filtration medium according to another embodiment of the present invention. The filtration medium (300) of FIG. 3 comprises a first non-woven fabric (301), a pollutant absorbent layer (302) comprising activated carbon fibers, a woven fabric (303) and a second non-woven fabric (304) needled together. The second non-woven fabric (304) is spaced apart from the first non-woven fabric (301) by the pollutant absorbent layer (302), and the woven fabric (303) is spaced apart from the pollutant absorbent layer (302) by the second non-woven fabric (304). The fluid inlet (305) and fluid outlet (306) surfaces of the filtration medium (300) comprise a coating which, in some embodiments, is operable to enhance the abrasion resistance of fibers protruding from the surfaces (305, 306) resulting from needling the filtration medium (300). In some embodiments, the coating is non-stick or repellant to particles in the fluid stream, thereby facilitating cleaning of the filtration medium (300) by techniques such as pulse jet or reverse air. In some embodiments, a membrane can be coupled (e.g., laminated) to the surface (305) of the non-woven fabric (301). The membrane can be, for example, a thin polytetrafluoroethylene film in some embodiments.

A filtration medium described herein, in some embodiments, comprises a pollutant absorbent layer comprising activated carbon fibers, a first non-woven fabric and a second non-woven fabric, wherein the pollutant absorbent layer is positioned between and needled to the first non-woven fabric and the second non-woven fabric. In some embodiments, a filtration medium comprises a woven fabric and a pollutant absorbent layer comprising a mixture of activated carbon fibers and structural fibers, wherein the pollutant absorbent layer is needled to the woven layer.

In some embodiments, and as discussed further below, a filtration medium (or certain components of the medium) can have a desirable gas or air permeability. Unless otherwise indicated, as used herein, gas permeability or air permeability values mentioned herein were measured using the ASTM D737 standard.

As noted above, in some embodiments, one or more of the non-woven fabric, the woven fabric, the pollutant absorbent layer, and/or other material layers may be needled together. Needling comprises passing materials through a needling device wherein a plurality of barbed needles are reciprocated up and down so as to penetrate the strands in the material (i.e. in the fabric, pollutant absorbent layer, other material layers, etc.) and thereby entangle them with one another.

The layers to be needled during assembly of a filtration medium can be needled using techniques known to those of ordinary skill in the art. Such techniques are further described in U.S. Pat. No. 3,713,962 (Ackley), U.S. Pat. No. 4,277,531 (Picone), U.S. Pat. No. 4,404,717 (Neubauer, et al.), and U.S. Pat. No. 4,964,891 (Schaefer), which are hereby incorporated by reference. In general, the needling conditions (including, for example, needle size) should generally be selected so as to provide adequate mechanical interlocking between the layers while generally seeking to avoid the presence of residual large holes in the filtration medium (e.g., holes that might permit large particulate matters in a gas stream to pass entirely through the filtration medium). Machines that can act as a suitable needling apparatus can be purchased from a variety of commercial suppliers including, for example, needling apparatuses from DILO Group, Germany. In some embodiments, the needles used in needling can be a small gauge needle, for example a 40 gauge needle. Suitable needles, for use in some embodiments, are model number 609901 needles from Groz-Beckert USA.

I. Non-Woven Fabric

Turning now to individual components that might be used in filtration media, filtration media described herein comprise at least one non-woven fabric.

In some embodiments, a non-woven fabric comprises glass fibers. Glass fibers suitable for use in the non-woven fabric can comprise any glass fiber not inconsistent with the objectives of the present invention. In some embodiments, suitable glass fibers comprise E-glass fibers, C-glass fibers, ECR glass fibers, S-glass fibers, zero-boron glass fibers or mixtures thereof.

In some embodiments, a non-woven fabric of a filtration medium described herein comprises synthetic polymeric fibers. Suitable synthetic polymeric fibers, in some embodiments, comprise acrylics, polyesters, polyamides, polyaramids, polyolefins, polyphenylene sulfide, polybenzimidazole, polyvinyl chloride, polyimides, carbon fibers, polyetherimide, fluoropolymers or mixtures thereof In some embodiments, synthetic polymeric fibers comprise various constructions including various monocomponent and bicomponent constructions.

In some embodiments, a non-woven fabric comprises natural fibers. Suitable natural fibers, in some embodiments, comprise cellulosics and derivatives thereof Additionally, in some embodiments, a non-woven fabric of a filtration medium described herein comprises inorganic fibers outside the scope of glass fibers. Suitable inorganic fibers, in some embodiments, comprise silica fibers, alumina fibers, alumina-silicate fibers, alumina-boro-silicate fibers, basalt fibers or mixtures thereof

In some embodiments, fibers of a non-woven fabric can have any diameter not inconsistent with the objectives of the present invention. Fibers of a non-woven fabric, in some embodiments, have an average diameter ranging from about 1 μm to about 30 μm. In some embodiments, fibers of a non-woven fabric have an average diameter ranging from about 2 μm to about 15 μm. In some embodiments, fibers of a non-woven fabric have an average diameter ranging from about 3 μm to about 10 μm or from about 5 μm to about 7 μm. In some embodiments, the non-woven fabric can be formed from D75 or D150 E-glass fiber glass strands.

A non-woven fabric can have any construction not inconsistent with the objectives of the present invention. In some embodiments, a non-woven fabric is provided as a non-woven mat of any of the foregoing fibers. In some embodiments, a non-woven fabric comprises one or more binders for the fibers. In some embodiments, binders comprise starch-oil binders or sizings, such as 610 or 8610 commercially available from PPG Industries of Pittsburgh, Pa.

Moreover, in some embodiments, a non-woven fabric can be subjected to post-formation treatments to enhance the resistance of the mat to various chemical conditions, such as acid or alkaline attack. In some embodiments, a post-formation treatment enhances the physical properties of the non-woven fabric, such as non-stick properties. A post-formation treatment can include exposing the non-woven fabric to a variety of chemical species such as polytetrafluoroethylene (PTFE), silicones, polyurethanes, epoxides, graphite or silanes or combinations thereof.

In some embodiments, a non-woven fabric of a filtration medium described herein has a thickness up to about 0.2 inch. A non-woven fabric, in some embodiments, has a thickness less than about 0.1 inch or less than about 0.05 inch. In some embodiments, a non-woven fabric has a weight of at least about 1 oz/yd². In some embodiments, a non-woven fabric has a weight of at least about 5 oz/yd². A non-woven fabric, in some embodiments, has a weight ranging from about 1 oz/yd² to about 15 oz/yd². In some embodiments, a non-woven fabric has a weight ranging from about 5 oz/yd² to about 10 oz/yd². In some embodiments, a non-woven fabric can have weight of between about 6 and about 30 oz/yd². The non-woven fabric can have a weight of between about 16 and 24 oz/yd² in some embodiments.

In some embodiments, a non-woven fabric demonstrates a permeability or porosity that minimizes pressure drop across the fabric and/or a filtration medium when the non-woven fabric is incorporated into the medium. A non-woven fabric, in some embodiments, has a permeability or porosity that is suitable for use in industrial flue gas filtration applications such as pulse jet or reverse air applications.

In some embodiments, a non-woven fabric has a permeability of at least about 80 scfm/ft² when measured using the ASTM D737 standard. A non-woven fabric, in some embodiments, has a permeability of at least about 100 scfm/ft² or a permeability of at least about 130 scfm/ft². In some embodiments, a non-woven fabric has a permeability of at least about 150 scfm/ft² or a permeability of at least about 200 scfm/ft². In some embodiments, a non-woven fabric has a permeability ranging from about 90 scfm/ft² to about 250 scfm/ft².

In some embodiments, the non-woven fabric is formed by wet laid processes using techniques known to those of ordinary skill in the art. In some embodiments, the non-woven fabric is formed by dry laid processes using techniques known to those of ordinary skill in the art.

II. Woven Fabric

In addition to at least one non-woven fabric layer, a filtration medium described herein, in some embodiments, comprises at least one woven fabric layer.

In some embodiments, a woven fabric layer comprises glass fibers, synthetic polymeric fibers, natural fibers or inorganic fibers or mixtures thereof. Glass fibers, polymeric fibers, natural fibers or inorganic fiber suitable for use in a woven fabric layer can comprise any of those recited in Section I hereinabove for a non-woven fabric layer. Moreover, in some embodiments, fibers of a woven fabric layer can have an average diameter consistent with any average fiber diameter recited in Section I hereinabove for a non-woven fabric layer. For example, as with the non-woven fabric, in some embodiments, the woven fabric can be formed from D75 or D150 E-glass fiber glass strands.

In some embodiments, a woven fabric comprises one or more binders for the fibers. In some embodiments, binders comprise starch-oil binders or sizings. In some embodiments, a woven fabric can be subjected to post-formation treatments to enhance the resistance of the fabric to various chemical conditions, such as acid or alkaline attack. In some embodiments, a post-formation treatment enhances the physical properties of the woven fabric, such as non-stick properties. A post-formation treatment can include exposing a woven fabric to a variety of chemical species such as polytetrafluoroethylene (PTFE), silicones, polyurethanes, epoxides, graphite or silanes or combinations thereof.

In some embodiments, a woven fabric of a filtration medium described herein has a thickness less than 0.2 inch. A woven fabric, in some embodiments, has a thickness less than about 0.1 inch or less than about 0.05 inch. In some embodiments, a woven fabric has a weight of at least about 1 oz/yd². In some embodiments, a woven fabric has a weight of at least about 5 oz/yd². A woven fabric, in some embodiments, has a weight ranging from about 1 oz/yd² to about 25 oz/yd². In some embodiments, a woven fabric has a weight ranging from about 5 oz/yd² to about 10 oz/yd². In some embodiments, a non-woven fabric can have weight of between about 6 and about 30 oz/yd². The non-woven fabric can have a weight of between about 16 and 24 oz/yd² in some embodiments.

In some embodiments, a woven fabric demonstrates a permeability or porosity that minimizes pressure drop across the fabric and/or assembled filtration medium. A woven fabric, in some embodiments, has a permeability or porosity that is suitable for use in industrial flue gas filtration applications, such as pulse jet applications or reverse air applications. In some embodiments, a woven fabric achieves desirable permeability and/or porosity by displaying a loose open weave structure. In some embodiments, a woven fabric is provided as a scrim. Additionally, a woven fabric, in some embodiments, uses low twist or no twist texturized yam to enhance permeability. In some embodiments, the woven fabric can formed from texturized yarns used in at least one direction (e.g., the warp direction). It is believed that using texturized yarn in at least one direction of the woven fabric to assist with the fabric's integration into the filtration medium during needling.

In some embodiments, a woven fabric has a permeability of at least about 100 scfm/ft² when measured using the ASTM D737 standard. A woven fabric, in some embodiments, has a permeability of at least about 150 scfm/ft² or a permeability of at least about 175 scfm/ft². In some embodiments, a non-woven fabric has a permeability of at least about 200 scfm/ft². In some embodiments, a woven fabric has a permeability ranging from about 100 scfm/ft² to about 250 scfm/ft².

III. Pollutant Absorbent Layer

A filtration medium described herein comprises a pollutant absorbent layer comprising activated carbon fibers. The pollutant absorbent layer, in some embodiments, is operable to remove one or more pollutants from a flue gas stream including, but not limited to, mercury and/or heavy metals. Moreover, in some embodiments, a pollutant absorbent layer of flue gas filtration medium described herein is operable to retain the absorbed pollutant indefinitely or for a desired time period. In some embodiments, a pollutant absorbent layer is operable to retain one or more pollutants when exposed to a variety of environmental conditions such as elevated temperatures associated with flue gas filtration applications.

Activated carbon fibers, in some embodiments, are produced from one or more synthetic polymeric fibers. In some embodiments, synthetic polymeric fibers suitable for producing activated carbon fibers comprise polyacrylonitrile fibers (PAN), phenolic fibers or polyvinyl alcohol fibers. In some embodiments, activated carbon fibers are produced from one or more natural fibers. Natural fibers suitable for producing activated carbon fibers, in some embodiments, comprise cellulosic fibers or rayon precursors.

In some embodiments, synthetic polymeric fibers and/or natural fibers are carbonized to produce activated carbon fibers. In some embodiments, synthetic polymeric and/or natural fibers are fully carbonized or partially carbonized. In one embodiment, for example, PAN fibers are partially carbonized, comprising about 20% to about 30% nitrogen from the precursor PAN.

In some embodiments, activated carbon fibers that can be used in the pollutant absorbent layer are commercially available in mat form as product numbers TK1000 or TK1600 from Jiangsu Tonkang Special Fabric & Garments Co., Ltd., China.

Activated carbon fibers of a pollutant absorbent layer can have any dimension not inconsistent with the objectives of the present invention. In some embodiments, activated carbon fibers have an average diameter ranging from about 10 nm to about 50 μm. In some embodiments, activated carbon fibers have an average diameter ranging from about 100 nm to about 30 μm. Activated carbon fibers, in some embodiments, have an average diameter of at least about 1 μm. In some embodiments, activated carbon fibers have an average diameter ranging from about 1 μm to about 20 μm or from about 5 μm to about 15 μm.

In addition to being commercially purchased in a mat form, in some embodiments, activated carbon fibers can be produced from synthetic polymeric and/or natural fiber derivatives produced by electrospinning techniques, such as those disclosed in United States Patent Application Publications 2008/0207798 and 2009/0102100, the disclosures of which are hereby incorporated by reference in their entireties. Such fibers can be assembled into mat form using techniques known to those of skill in the art.

In some embodiments, carbon fibers can be activated or further activated by various physical and chemical methods. In some embodiments, the physical methods commonly include the presence of carbon dioxide or water vapor under controlled atmospheres and at elevated temperatures. Alternatively, many activation procedures use dehydrating agents such as zinc chloride or phosphoric acid to accomplish activation at temperatures between about 400 to about 700° C. Potassium hydroxide can be used after activation, in some embodiments, to further open the pores in the carbon fibers resulting in a larger pore size distribution.

In some embodiments, activated carbon fibers can also be treated with a retention species operable to inhibit or preclude the desorption or release of one or more pollutants (e.g., mercury) captured by the fibers during flue gas filtration. In some embodiments, for example, activated carbon fibers can be impregnated with various forms of sulfur, chlorine, bromine and/or iodine including, for example, elemental sulfur, to inhibit or preclude the desorption or release of mercury captured from a flue gas stream.

In some embodiments, a pollutant absorbent layer of a flue gas filtration medium described herein comprises at least 1% by weight sulfur. In some embodiments, a pollutant absorbent layer comprises sulfur in an amount ranging from about 2 weight percent to about 30 weight percent. In some embodiments, a pollutant absorbent layer comprises sulfur in an amount ranging from about 5 weight percent to about 15 weight percent. In some embodiments, a pollutant absorbent layer comprises sulfur in an amount ranging from about 18 weight percent to about 25 weight percent.

In some embodiments, a pollutant absorbent layer comprises bromine as a mercury retention species in an amount of at least about 1 weight percent. In some embodiments, a pollutant absorbent layer comprises bromine in an amount of at least about 5 weight percent. A pollutant absorbent layer, in some embodiments, comprises chlorine as a mercury retention species in an amount of at least about 1 weight percent. A pollutant absorbent layer, in some embodiments, comprises chlorine as a mercury retention species in an amount of at least about 5 weight percent. In some embodiments, a pollutant absorbent layer comprises iodine as a mercury retention species in an amount of at least about 1 weight percent. In some embodiments, a pollutant absorbent layer comprises iodine in an amount of at least about 5 weight percent.

In some embodiments, residues from the activation process can also be useful as mercury retention species. For example, in some embodiments, the carbonized fibers (in mat form or otherwise) can be exposed to solutions of zinc chloride as an activating agent. Residues of the zinc chloride are then capable of oxidizing and retaining mercury in the activated carbon in some embodiments. In some embodiments, activated carbon fibers can comprise zinc in an amount of at least about 0.25 weight percent. Activated carbon fibers, in some embodiments, can comprise zinc in an amount up to about 6 weight percent.

In some embodiments, to incorporate the retention species in the pollutant absorbent layer, the pollutant absorbent layer comprising activated carbon fibers (in mat form or otherwise) can be subjected to chemical treatment by metal salts comprising potassium chloride, potassium bromide, potassium iodide, zinc bromide, zinc chloride, or combinations thereof. In some embodiments, for example, the metal salts can be applied to a mat of activated carbon fibers as aqueous solutions comprising an amount of metal salt corresponding to between about 5 and about 100% of the carbon mass in the pollutant absorbent layer.

In some embodiments, the pollutant absorbent layer can be heated in an oven after treatment with the metal salts. In some such embodiments, the pollutant absorbent layer is heated for from about 1 to about 7 hours. In some such embodiments, the pollutant absorbent layer is heated at a temperature of about 150° C. to about 950° C. In some such embodiments, the pollutant absorbent layer is heated at between about 150° C. to about 250° C. or about 450° C. to about 500° C.

In some embodiments, activated carbon fibers are impregnated with noble metals including, for example, platinum, palladium, gold or silver or alloys thereof.

A mercury retention species when applied to activated carbon fibers in mat form, in some embodiments, is operable to inhibit or preclude desorption or release of captured mercury when the pollutant absorbent layer is heated to temperatures of up to about 550° F. In some embodiments, a mercury retention species applied to activated carbon fibers is operable to inhibit or preclude desorption or release of captured mercury when the pollutant absorbent layer is heated to temperatures of up to about 500° F. In some embodiments, a mercury retention species applied to activated carbon fibers is operable to inhibit or preclude desorption or release of captured mercury when the pollutant absorbent layer is heated to temperatures of up to about 400° F.

In some embodiments, a pollutant absorbent layer comprising activated carbon fibers can have a surface area ranging from about 150 m²/g to about 2600 m²/g. In some embodiments, a pollutant absorbent layer comprising activated carbon fibers can have a surface area ranging from about 100 m²/g to about 600 m²/g. In some embodiments, a pollutant absorbent layer comprising activated carbon fibers can have a surface area ranging from about 1200 m²/g to about 1700 m²/g. A pollutant absorbent layer comprising activated carbon fibers, in some embodiments, can haves a surface area ranging from about 1300 m²/g to about 1600 m²/g. Surface areas of pollutant absorbent layers described herein are determined according to BET theory and techniques. Unless otherwise stated, references to surface area herein reflect measurement of surface area according to ASTM D6556-10 Standard Method for Carbon Black Total and External Surface Area by Nitrogen Absorption.

The amount of mercury retention per gram of activated carbon fiber sorbent under static conditions of room temperature and saturated mercury vapor can be measured according to the following procedure: 50 mg of pollutant absorbent material was sealed into a fiberglass pocket that provided physical protection while allowing air flow. The sample was suspended by hanging in the vapor phase of a 1 quart jar with a quantity of liquid elemental mercury in the bottom. The jar was sealed and stored at room temperature for 7 days, after which, the sample was removed from the jar and placed in an airtight plastic bag. The sample was tested for total mercury content by Direct Mercury Analysis (DMA). DMA analysis was performed by IMR Test Labs using their CAP-054E (DMA) procedure. Unless otherwise stated herein, references to static mercury retention values herein (mercury retention per gram of activated carbon fiber sorbent) reflect measurements taken using this procedure.

In some embodiments, a pollutant absorbent layer demonstrates a capacity for absorbing at least about 50 mg of mercury per gram of the activated carbon fiber sorbent under static conditions of room temperature in saturated mercury vapor. Some embodiments of a pollutant absorbent layer can demonstrate a capacity for absorbing at least about 100 mg of mercury per gram of the activated carbon fiber sorbent under static conditions of room temperature in saturated mercury vapor, as measured using the same procedure. A pollutant absorbent layer, in some embodiments, can demonstrate a capacity for absorbing at least about 150 mg of mercury per gram of the activated carbon fiber sorbent under static conditions of room temperature in saturated mercury vapor, as measured using the same procedure. Some embodiments of a pollutant absorbent layer can demonstrate a capacity for absorbing at least about 200 mg of mercury per gram of the activated carbon fiber sorbent under static conditions of room temperature in saturated mercury vapor, as measured using the same procedure.

In some embodiments, a pollutant absorbent layer demonstrates a capacity for absorbing at least about 6 mg of mercury per gram of the activated carbon fiber sorbent over a period of five days under conditions of dynamic air flow at 350° F., the air comprising 11 ppb mercury vapor. In some embodiments, a pollutant absorbent layer demonstrates a capacity for absorbing at least about 10 mg of mercury, at least about 15 mg of mercury, at least about 20 mg of mercury, or at least about 25 mg of mercury per gram of the activated carbon fiber sorbent under conditions of dynamic dry nitrogen flow at 300° F. for 140 hours at a mercury vapor concentration of 75 ppb and a 4 fpm gas velocity through the sample.

A pollutant absorbent layer comprising activated carbon fibers can have any dimensions not inconsistent with the objectives of the present invention. In some embodiments, a pollutant absorbent layer can have a thickness ranging from about 0.01 inch to about 0.3 inch. In some embodiments, a pollutant absorbent layer can have a thickness ranging from about 0.02 inch to about 0.1 inch. The pollutant absorbent layer can have a thickness of between about 0.1 inches to about 0.2 inches in some embodiments.

In some embodiments, a pollutant absorbent layer comprising activated carbon fibers has a gas permeability of at least about 20 scfm/ft². A pollutant absorbent layer, in some embodiments, has a gas permeability of at least about 25 scfm/ft². In some embodiments, a pollutant absorbent layer has a gas permeability ranging from about 15 scfm/ft² to about 120 scfm/ft² or from about 20 scfm/ft² to about 80 scfm/ft².

In some embodiments, the basis weight of a pollutant absorbent layer comprising activated carbon fibers ranges from about 1 g/ft² to about 60 g/ft². A pollutant absorbent layer, in some embodiments, has a basis weight ranging from about 5 g/ft² to about 30 g/ft². In some embodiments, a pollutant absorbent layer has a basis weight ranging from about 20 g/ft² to about 30 g/ft².

In some embodiments, the fibers comprising the pollutant absorbent layer have a diameter less than about 15 microns, which can allow for improved airflow and increased surface area, thereby improving sorption kinetics. Without being bound by theory, the improved sorption kinetics are believed to be due to increased collision frequency. In some embodiments, the fibers comprising the pollutant absorbent layer can have multi-lobal cross sections (e.g. fibers from viscose rayon), which also provide increased surface area.

IV. Fluid Inlet/Outlet Coating and Membrane

In some embodiments, fluid inlet surfaces and/or fluid gas outlet surfaces of a filtration medium described herein can comprise a coating. In general, the coating may be applied to one or more layers of the filtration medium. In some embodiments, a coating can be operable to enhance the abrasion resistance of fibers protruding from a gas inlet and/or outlet surface resulting from needling the filtration medium. In some embodiments, the coating is non-stick or repellant to particles in the fluid stream, thereby facilitating cleaning of the filtration medium by techniques such as pulse jet or reverse air.

The coating can provide one or more functions depending on the coating selected and the desired characteristics. For example, and without limitation, various coatings can provide abrasion resistance, can assist in bonding of layers, can provide chemical resistance, and/or can provide non-stick properties. Moreover, in some embodiments, a coating can enhance the resistance of an fluid inlet and/or outlet surface to moisture, acid and/or alkaline species.

A coating for fluid gas inlet and/or outlet surfaces of a filtration medium can have any thickness not inconsistent with the objectives of the present invention. In some embodiments, a coating can have a thickness less than about 5 μm. In some embodiments, a coating can have a thickness ranging from about 1 μm to about 3 μm. A coating, in some embodiments, can have a thickness less than about 1 μm.

In selecting a coating and a coating thickness, one should generally avoid coatings on a fluid inlet surface and/or fluid outlet surface that would generally occlude or substantially occlude the pore structure of the surface so as to maintain acceptable or desirable gas flow characteristics though the surface and the filtration medium.

In some embodiments, the coating can comprise one or more of the following: at least one urethane, at least one silicone, at least one fluorocarbon, at least one epoxy, at least one silane, or at least one siloxane, or combinations thereof. In some embodiments, urethane coatings can provide bonding, chemical resistance, and/or abrasion resistance. Fluorocarbons, in some embodiments can provide abrasion resistance and/or high temperature stability. In some embodiments, epoxies can provide bonding, chemical resistance, and/or abrasion resistance. Silicones, silanes and/or siloxanes can provide bonding. In some embodiments where the coating comprises fluorocarbons, the fluorocarbon can comprise polytetrafluoroethylene (PTFE). A PTFE coating, in some embodiments, can provide non-stick properties, abrasion resistance, and/or chemical resistance. For example, the non-stick property can be useful in promoting the easy release of fly ash particles when the filtration medium is subject to a cleaning cycle as well as enhancing the filtration of particles smaller than 2.5 μm. In some embodiments, coating materials that provide adhesive bonding can strengthen non-woven media and promote adhesion between a non-woven fabric and the absorbent layer.

In some embodiments, the filtration medium can further comprise a membrane attached to a fluid inlet surface or a fluid outlet surface. In some embodiments, the membrane can be coupled (e.g., laminated) at the fluid inlet surface. In some embodiments, the membrane can comprise polyester, vinyl polymers, polyethylene, cellulose fibers, fluorocarbons, or combinations thereof. In one embodiment, the membrane comprises expanded polytetrafluoroethylene (ePTFE). In some embodiments, the membrane coupled to a non-woven fabric layer by heat lamination using calendar rolls. In some embodiments, the membrane has a pore size and thickness that improves filtration efficiency of 2.5 micron particles (e.g. removes particles having a size of 2.5 microns or larger from a fluid stream). Suitable membranes for use in embodiments of the present invention can be obtained from and laminated onto the filtration medium by TTG Inc. of Higginsville, Mo.

In some embodiments, the filtration medium can comprise both a coating and a membrane coupled to the fluid inlet surface.

V. Assembled Filtration Medium

In some embodiments, filtration media described herein are assembled by methods described herein In some embodiments, a filtration medium described herein has a thickness ranging from about 0.05 inch to about 0.5 inch. In some embodiments, a filtration medium has a thickness ranging from about 0.1 inch to about 0.3 inch.

In some embodiments, a filtration medium described herein has a permeability of at least about 10 scfm/ft². In some embodiments, a filtration medium has a permeability ranging from about 15 scfm/ft² to about 70 scfm/ft². A filtration medium, in some embodiments, has a permeability ranging from about 20 scfm/ft² to about 50 scfm/ft².

A filtration medium, in some embodiments, has sufficient strength and/or mechanical integrity to permit use of the filtration medium in pulse jet or reverse air filtration applications. In some embodiments, a filtration medium described herein has a tensile strength of at least about 200 lbf/2″ as determined according to ASTM D5035. In some embodiments, a filtration medium described herein has a tensile strength of at least about 225 lbf/2″. In some embodiments, a filtration medium has a tensile strength ranging from about 200 lbf/2″ to about 300 lbf/2″.

A filtration medium described herein, in some embodiments, has a MIT Flex count of at least about 300,000 relative to the width of the filtration medium according to ASTM D2176. In some embodiments, a filtration medium described herein has a MIT Flex count of at least about 800,000 relative to the length of the filtration medium according to ASTM D2176.

A filtration medium described herein, in some embodiments, removes at least a portion of mercury present in a flue gas when the flue gas is passed through the filtration medium. The amount of mercury removed can be measured according to the following procedure: a mercury-laden gas stream is prepared by running dry nitrogen through a glass U-tube incorporating a mercury permeation tube commercially available from VICI (Valco Instruments Co. Inc.). The U-tube is held in a controlled-temperature oil bath to control the mass flow-rate of mercury from the permeation tube. The mercury-laden nitrogen stream is then passed through a length of tubing in a heated chamber to reach the desired test temperature. A sorbent sample is held in place by a commercially available membrane filter holder such as those used in the HPLC field, where the sample replaced the filter. The sample is exposed to the heated, mercury-laden nitrogen and the gas downstream of the sample is analyzed in real time by a cold vapor atomic absorption instrument to determine breakthrough concentration of mercury. The inlet concentration of mercury is measured using the same instrument both before and after the absorption experiment. References to mercury removal from a flue gas stream (or dynamic mercury removal) herein will refer to mercury removal according to this procedure unless stated otherwise.

In some embodiments, a flue gas filtration medium removes at least about 50 percent of mercury in a flue gas. In some embodiments, a flue gas filtration medium removes at least about 70 percent of mercury in a flue gas. A flue gas filtration medium, in some embodiments, removes at least about 90 percent or at least about 95 percent of mercury in a flue gas. In some embodiments, a flue gas filtration medium described herein removes up to 100 percent of mercury in a flue gas.

Moreover, in some embodiments, a flue gas filtration medium retains at least a portion of the captured or absorbed mercury for a time period of at least one year based on accelerated experiments. Acceleration is typically accomplished by increasing the mercury vapor concentration (typically up to 75 times the value commonly seen in industrial flue gas emissions). In some embodiments, a flue gas filtration medium retains at least a portion of the captured or absorbed mercury for a period of at least three years. In some embodiments, the portion of mercury retained will depend on various environmental conditions and factors to which the flue gas filtration medium is exposed. In some embodiments, a flue gas filtration medium described herein retains greater than 90% or greater than 95% of the mercury captured when the filtration medium is exposed to temperatures up to about 500° F. In some embodiments, a flue gas filtration medium described herein retains all or substantially all of the mercury captured when the filtration medium is exposed to temperatures up to about 500° F.

VI. Pulse Jet and Reverse Air Flue Gas Filtration System

Filtration media described herein, in some embodiments, are suitable for use in pulse jet and/or reverse air processes. In some embodiments, a pulse jet flue gas filtration system is provided. In some embodiments, the pulse jet flue gas filtration system comprises a flue gas inlet manifold, a flue gas outlet manifold and a plurality of filtration apparatus positioned between the inlet manifold and the outlet manifold, wherein at least one of the plurality of filtration apparatus comprises a wire cage support and a filtration medium disposed over the wire cage support. The filtration medium disposed over the wire cage support can comprise any one of the filtration media constructions described herein.

In some embodiments, a filtration medium described herein is in the shape of a bag for assembly over the wire cage support or for coupling to one or more support rings. In some embodiments, a blowpipe and orifice is proximate to the filtration medium for providing pulses of compressed air into the filtration medium for the removal of particles on the inlet surfaces of the filtration media.

FIG. 4 illustrates filtration apparatus of a pulse jet filtration system according to one embodiment of the present invention. FIG. 4( a) illustrates flue gas filtration media (402, 404) having a construction described herein executing filtration of a flue gas stream (405). As illustrated in FIG. 4( a), the filtration media (402, 404) are formed into bags for positioning over wire cage supports (406). The flue gas (405) flows through the filtration media (402, 404), thereby depositing various particulate matter (407) on surfaces of the filtration media (402, 404). As described herein, in some embodiments, the filtration media (402, 404) also removes one or more metal pollutants, such as mercury, upon passage of the flue gas (405) through the filtration media (402, 404).

FIG. 4( b) illustrates cleaning of the flue gas filtration media (402, 404). During the cleaning process, a pulse (410) of air or gas is provided by a blowpipe (412) and orifice (414) to the interiors of the gas filtration media (402, 404) causing the filtration media (402, 404) to expand and flex. The expansion and flexion of the filtration media (402, 404) dislodges the particulate matter (407) on surfaces of the filtration media (402, 404). The dislodged particulate matter (407) can be collected in hoppers (not shown) located beneath the filtration media (402, 404).

In another embodiment, a reverse air flue gas filtration system is provided. The reverse air flue gas filtration system comprises a flue gas inlet manifold, a flue gas outlet manifold and a plurality of filtration apparatus positioned between the inlet manifold and the outlet manifold, wherein at least one of the plurality of filtration apparatus comprises one or more support rings and a filtration medium coupled to the one or more support rings. The filtration medium coupled to the one or more support rings can comprise any one of the filtration media described herein.

VII. Methods of Producing Filtration Media

In another aspect, the present invention provides methods of producing filtration media. In some embodiments, a method of producing a filtration medium comprises providing a pollutant absorbent layer comprising activated carbon fibers, a first non-woven fabric and a at least one woven fabric, positioning the pollutant absorbent layer between the first non-woven fabric and woven fabric and needling the first non-woven fabric, pollutant absorbent layer and the woven fabric. In some embodiments, a method of producing a filtration medium further comprises providing a second non-woven fabric and positioning the second non-woven fabric adjacent to the woven fabric prior to needling. In some embodiments, woven fabric is positioned between the second non-woven fabric and the pollutant absorbent layer. In some embodiments, the second non-woven fabric is positioned between the woven fabric and the pollutant absorbent layer.

A method of producing a filtration medium, in some embodiments, comprises providing a first non-woven fabric, a second-nonwoven fabric and a pollutant absorbent layer comprising activated carbon fibers, positioning the pollutant absorbent layer between the first non-woven fabric and the second non-woven fabric and needling first non-woven fabric, pollutant absorbent layer and second non-woven fabric.

In some embodiments, a method of producing a filtration medium comprises providing a woven fabric and a pollutant absorbent layer comprising a mixture of activated carbon fibers and structural fibers and needling the pollutant absorbent layer and the woven fabric.

In some embodiments of methods of producing a filtration medium, needling comprises needling one or both sides of the filtration medium. In some embodiments, needling conditions are chosen to entrap protruding fibers in one or both needling directions.

A method of producing a filtration medium, in some embodiments, further comprises applying a coating to a fluid inlet surface of the filtration medium. In some embodiments, a method of producing a filtration medium further comprises applying a coating to a fluid outlet surface of the filtration medium. A coating, as described herein in some embodiments, can increase the abrasion and chemical resistance of fibers protruding above the gas inlet and/or outlet surfaces, thereby increasing the durability of the filtration medium.

In some embodiments, a method of producing a filtration medium comprises attaching a membrane to a fluid inlet surface or a fluid outlet surface, as described above.

The filtration medium, in some embodiments, can perform well when subjected to ETS particulate testing according to ASTM D6830-02. In some embodiments, the filtration medium had a PM2.5 (g/dscm) of <1.67×10⁻⁵, an average residual ΔP (cm w.g.) ranging between 2.6 and 3.0, and with a number of cleaning cycles ranging between 95 and 110.

VIII. Methods of Treating a Flue Gas

In another aspect, the present invention provides methods of treating a flue gas. In some embodiments, a method of treating flue gas comprises providing a filtration medium described herein and flowing the flue gas through the filtration medium, wherein at least a portion of mercury in the flue gas is removed by the filtration medium. In some embodiments, at least 50 percent of the mercury in the flue gas is removed by the filtration medium. In some embodiments, at least 70 percent of the mercury in the flue gas is removed by the filtration medium. In some embodiments, at least 90 percent or at least 95 percent of the mercury in the flue gas is removed by the filtration medium. In some embodiments, all or substantially all of the mercury in the flue gas is removed by the filtration medium.

In some embodiments, a method of treating a flue gas further comprises at least partially removing a particulate component of the flue gas stream when the flue gas stream is passed through the filtration medium. In some embodiments greater than 90 percent of the particulate component of the flue gas is removed. In some embodiments, all or substantially all of the particulate component of the flue gas is removed.

These and other embodiments of flue gas filtration media are further illustrated by the following non-limiting examples.

EXAMPLE 1 Preparation of a Pollutant Absorbent Layer

A non-woven mat comprising PAN fibers was oxidized and annealed by placing between fiberglass sheets on a perforated tray in a muffle furnace preheated to 150° C. 5 scfh of house air was supplied into the furnace as a purge gas. The sample was heated at 2 C/min to 240° C., held at 240° C. for 2 hours, purged with 20 scfh N₂ for 30 minutes, heated to 350° C. at 2° C./min, held at 350° C. for 1 hour, then cooled to below 250° C. before removing from the oven and rapidly cooling.

The annealed PAN mat was further activated by soaking in a 9% aqueous solution of zinc chloride for 30 minutes, drying in a 120° C. convection oven for 18 hours, loading into a tube furnace preheated to 200° C., holding at 200° C. for 30 minutes under a nitrogen purge of 20 scfh, heating to 600° C. at a rate of 10° C./min, holding at 600° C. for 30 minutes, cooling to below 200° C. and removing. The treated sample was washed with a 0.5N HCl solution followed by DI (de-ionized) water to remove unreacted zinc chloride.

The sample was evaluated by nitrogen porosimetry and determined to have a BET surface area of 381 m²/g. The sample had a room temperature static mercury sorption under saturated mercury vapor after one week of 41 mg/g. Dynamic mercury sorption performed under forced flow conditions in air at 350° F. with 11 ppb mercury vapor yielded 6 mg/g uptake before loss in efficiency.

EXAMPLE 2

A pollutant absorbent layer comprising a TK1600 carbon fiber mat (obtained from Jiangsu Tonkang Special Fabric & Garments Co., Ltd., China) was further treated by soaking it in 1% aqueous zinc chloride solution for 1 minute and drying in an oven with nitrogen purge gas for 1 hour at 200° C. The sample was measured to have a BET surface area of 1269 m²/g according to ASTM D6556-10. Elemental analysis by x-ray photoelectron spectroscopy showed the sample to have 5.8 atom % of chlorine incorporated. Room temperature static mercury absorption was 69 mg of mercury per gram of carbon as measured by the procedure described in paragraph [0080] above.

EXAMPLE 3

A pollutant absorbent layer comprising TK1600 carbon fiber mat (obtained from Jiangsu Tonkang Special Fabric & Garments Co., Ltd., China) was further treated by soaking it in 10% aqueous potassium bromide solution for 1 minute and drying in an oven with nitrogen purge gas for 6 hours at 475° C. The sample was measured to have a BET surface area of 558 m²/g according to ASTM D6556-10. Elemental analysis by x-ray photoelectron spectroscopy showed the sample to have 4.0 atom % of bromine incorporated. Room temperature static mercury absorption was 68 mg of mercury per gram of carbon as measured by the procedure described in paragraph [0080] above.

EXAMPLE 4

A pollutant absorbent layer comprising TK1600 carbon fiber mat (obtained from Jiangsu Tonkang Special Fabric & Garments Co., Ltd., China), roughly 6″ by 12″ in size was further treated by sprinkling with elemental sulfur powder uniformly over the surface in a mass ratio of about 1:1 carbon:sulfur. The carbon and sulfur were rolled into a tube shape and placed inside a 6″ diameter quartz tube furnace, purged with dry nitrogen, and heated at 10° C./min up to a final temperature of 470° C. The sample was held at 470° C. for one hour before cooling and removing from the tube furnace. The sample was measured to have a BET surface area of 1268 m²/g according to ASTM D6556-10. Elemental analysis by x-ray photoelectron spectroscopy showed the sample to have 9.3 atom % of sulfur incorporated into the surface. Room temperature static mercury absorption was 52 mg of mercury per gram of carbon as measured by the procedure described in paragraph [0080] above.

EXAMPLE 5

A non-woven mat comprising PAN fibers was oxidized and annealed by placing it between fiberglass sheets on a perforated tray in a muffle furnace preheated to 150° C. 5 scfh of house air was supplied into the furnace as a purge gas. The sample was heated at 2° C./min to 240° C., held at 240° C. for 2 hours, purged with 20 scfh N₂ for 30 minutes, heated to 350° C. at 2° C./min, held at 350° C. for 1 hour, then cooled to below 250° C. before removing from the oven and rapidly cooling.

The annealed PAN mat was further activated by dipping in 5% aqueous zinc chloride solution for 1 minute followed by drying at 80° C. in a convection oven. The dried sample was then placed into a quartz tube furnace, purged with dry nitrogen, and heated at 10° C./min up to a final temperature of 900° C. The sample was held at 900° C. for 5 minutes before cooling and removing from the tube furnace. The sample was measured to have a BET surface area of 399 m²/g according to ASTM D6556-10. Elemental analysis by x-ray photoelectron spectroscopy showed the sample to have 3.1 atom % of chlorine incorporated into the surface. Room temperature static mercury absorption was 148 mg of mercury per gram of carbon as measured by the procedure described in paragraph [0080] above.

EXAMPLE 6

A sample of activated carbon fiber mat prepared in accordance with Example 1 was impregnated with elemental sulfur by combining with excess sulfur (20:1 sulfur to sample mass) in close contact in a crucible heated under a nitrogen environment to 500° C. at a rate of 10° C./min, held at 500° C. for 1 hour and cooled to below 200° C. before removal. Surface elemental analysis using X-ray fluorescence spectroscopy (XPS) determined that the sulfur uptake by the activated carbon mat was 11% by mass, with no change in visual appearance of the sample. Similar experiments at 400° C. and 600° C. yielded 10% and 6% respectively. BET surface area was measured to be 59, 235, and 220 m²/g for the samples treated at 400, 500, and 600° C. respectively according to ASTM D6556-10. Room temperature static mercury absorption was measured to be 23, 22, and 19 mg of mercury per gram carbon for the samples treated at 400, 500, and 600° C., respectively, as measured by the procedure described in paragraph [0080] above.

EXAMPLE 7

As described above, in some embodiments, one or more of a non-woven fabric, a woven fabric, a pollutant absorbent layer, and/or other material layers can be needled together. When the non-woven fabric and the woven fabric are formed from fiber glass, exemplary needling techniques for needling the layers with a pollutant absorbent layer are set forth in this Example. For each of the samples, a non-woven fiber glass mat, a woven fiber glass mat, and a pollutant absorbent layer were needled together. The needling was performed on as needler device manufactured by DILO Group. The needles that were used for each of the samples were model number 609901 needles from Groz-Beckert USA. Table 1 describes the operating parameters for the needling of the different samples. In addition to the parameters listed in Table 1, the following parameters were common to each of the samples described in Table 1: model 609901 needles from Groz-Beckert USA; 50 needles/linear inch; 385 strokes/minute; 308 punches/in² in one pass.

TABLE 1 Sample Number Parameter 1 2 3 4 5 6 7 8 Passes 1 2 2 4 1 2 2 4 Penetration 8 8 8 8 6 6 6 6 (mm) Working 5 5 5 5 3 3 3 3 Barbs Needle Board down down, down, down, down down, down, down, Simulation down up up, down up up, down, down, up up Total 308 616 616 1232 308 616 616 1232 Punches/in²

Desirable characteristics, which can be exhibited by embodiments of the present invention, can include, but are not limited to, the provision of filtration media that can effectively remove pollutants from an air or gaseous stream; the provision of filtration media that can effectively remove mercury from an air or gaseous stream; the provision of filtration media that can effectively retain mercury or other pollutants that have been captured from an air or gaseous stream; the provision of filter media that can effectively remove and retain mercury from an air or gaseous stream at industrially relevant temperatures; the provision of filtration media that can effectively remove mercury or other pollutants from an air or gaseous stream while providing sufficient and/or desirable air or gas permeability; the provision of filtration media that can effectively remove mercury or other pollutants from an air or gaseous stream while providing sufficient and/or desirable mechanical properties; the provision of filtration media that can effectively remove mercury or other pollutants from an air or gaseous stream while having a sufficient or desirable lifespan; the provision of useful methods for assembling filtration media; the provision of useful methods for removing mercury or other pollutants from an air or gaseous stream; and others.

Various embodiments of the invention have been described in fulfillment of the various objects of the invention. It should be recognized that these embodiments are merely illustrative of the principles of the present invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention. 

That which is claimed:
 1. A filtration medium comprising: a pollutant absorbent layer comprising a mat comprising a plurality of activated carbon fibers; at least one woven fabric; and at least one non-woven fabric; wherein the pollutant absorbent layer is positioned between the at least one woven fabric and the at least one non-woven fabric, wherein the at least one woven fabric and the at least one nonwoven fabric are fiber glass fabrics, and wherein the pollutant absorbent layer further comprises metal halide salts, metal hydroxides, inorganic acids, or combinations thereof.
 2. The filtration medium of claim 1, wherein the pollutant absorbent layer is needled to the at least one woven fabric and the at least one non-woven fabric.
 3. The filtration medium of claim 1, wherein the filtration medium further comprises a second non-woven fabric.
 4. The filtration medium of claim 3, wherein the second non-woven fabric is positioned on an opposite side of the pollutant absorbent layer from the at least one non-woven fabric.
 5. The filtration medium of claim 3, wherein the at least one non-woven fabric, the pollutant absorbent layer, the woven fabric, and the second non-woven fabric are needled together.
 6. The filtration medium of claim 1, wherein the at least one woven fabric and the at least one nonwoven fabric comprise E-glass fibers, C-glass fibers, ECR glass fibers, S-glass fibers, zero-boron glass fibers or mixtures thereof.
 7. The filtration medium of claim 1, wherein the at least one non-woven fabric has a thickness up to about 0.2 inches.
 8. The filtration medium of claim 1, wherein the at least one non-woven fabric has a permeability of at least about 80 scfm/ft² according to ASTM D
 737. 9. The filtration medium of claim 1, wherein the at least one woven fabric has a thickness up to about 0.2 inches.
 10. The filtration medium of claim 1, wherein the at least one woven fabric has a permeability of at least about 100 scfm/ft² according to ASTM D
 737. 11. The filtration medium of claim 1, wherein the activated carbon fibers comprise synthetic polymeric fibers, natural fibers, or combinations thereof
 12. The filtration medium of claim 11, wherein the synthetic polymeric fibers comprise polyacrylonitrile fibers, phenolic fibers, polyvinyl alcohol fibers, or combinations thereof
 13. The filtration medium of claim 11, wherein the natural fibers comprise cellulosic fibers or rayon precursors.
 14. The filtration medium of claim 1, wherein the activated carbon fibers are partially carbonized.
 15. The filtration medium of claim 1, wherein the pollutant absorbent layer comprises metal halide salt and the metal halide salt comprises zinc chloride, zinc bromide, or combinations thereof.
 16. The filtration medium of claim 15, wherein the zinc chloride or zinc bromide is present in amount ranging from about 0.25 to about 6 weight percent zinc.
 17. The filtration medium of claim 1, wherein the pollutant absorbent layer comprises metal halide salt and wherein the metal halide salt comprises potassium chloride, potassium bromide, potassium iodide, or combinations thereof.
 18. The filtration medium of claim 1, wherein the activated carbon fibers have an average diameter ranging of up to about 50 μm.
 19. The filtration medium of claim 1, wherein the activated carbon fibers have an average diameter of at least about 100 nm.
 20. The filtration medium of claim 1, wherein the activated carbon fibers further comprise at least one mercury retention species.
 21. The filtration medium of claim 20, wherein the at least one mercury retention species comprises sulfur or a halogen.
 22. The filtration medium of claim 20, wherein the mercury retention species comprises iodine, bromine, or chlorine.
 23. The filtration medium of claim 21, wherein the mercury retention species comprises bromine.
 24. The filtration medium of claim 22, wherein the mercury retention species is present in an amount of at least 1 weight percent.
 25. The filtration medium of claim 22, wherein the mercury retention species is present in an amount of at least 5 weight percent.
 26. The filtration medium of claim 1, wherein the pollutant absorbent layer has a surface area of at least about 150 m²/g as measured by ASTM D 6556-
 10. 27. The filtration medium of claim 1, wherein the pollutant absorbent layer absorbs at least about 50 mg of mercury per gram of activated carbon fiber at room temperature in saturated mercury vapor.
 28. The filtration medium of claim 1, wherein the pollutant absorbent layer absorbs at least about 100 mg of mercury per gram of activated carbon fiber at room temperature in saturated mercury vapor.
 29. The filtration medium of claim 1, wherein the pollutant absorbent layer has a permeability of at least about 20 scfm/ft² according to ASTM D
 737. 30. The filtration medium of claim 1, wherein the filtration medium comprises a fluid inlet surface and a fluid outlet surface, and wherein at least one of the fluid inlet surface and the fluid outlet surface further comprises a coating.
 31. The filtration medium of claim 30, wherein the coating comprises a non-stick coating.
 32. The filtration medium of claim 30, wherein the coating comprises at least one urethane, at least one silicone, at least one fluorocarbon, at least one epoxy, at least one silane, or at least one siloxane, or combinations thereof
 33. The filtration medium of claim 30, wherein the coating comprises polytetrafluoroethylene.
 34. The filtration medium of claim 1, wherein the filtration medium has a thickness of at least about 0.1 inches.
 35. The filtration medium of claim 34, wherein the filtration medium has a thickness of less than about 0.5 inches.
 36. The filtration medium of claim 1, wherein the filtration medium has a permeability of at least about 10 scfm/ft² according to ASTM D
 737. 37. The filtration medium of claim 1, wherein the filtration medium has a tensile strength of at least about 200 lbf/2 inches according to D5035.
 38. The filtration medium of claim 1, wherein the filtration medium has a MIT Flex count of at least about 300,000 relative to the width of the filtration medium.
 39. The filtration medium of claim 1, further comprising a membrane coupled to the at least one non-woven fabric.
 40. The filtration medium of claim 39, wherein the membrane comprises polytetrafluoroethylene.
 41. A filtration system comprising: a flue gas inlet manifold; a flue gas outlet manifold; and at least one filtration apparatus positioned between the flue gas inlet manifold and the flue gas outlet manifold, the at least one filtration apparatus comprising the filtration medium of claim 1 disposed over a wire cage support.
 42. The filtration system of claim 41, wherein the filtration medium is in the shape of a bag.
 43. The filtration system of claim 41, wherein the at least one filtration apparatus further comprises at least one support ring operatively coupled to the filtration medium.
 44. A filtration medium comprising: a pollutant absorbent layer comprising a mat comprising a plurality of activated carbon fibers treated with a mercury retention species; at least one woven fiber glass fabric; and at least one non-woven fiber glass fabric; wherein the pollutant absorbent layer is positioned between the at least one woven fabric and the at least one non-woven fabric and wherein the pollutant absorbent layer is needled to the at least one woven fabric and the at least one non-woven fabric.
 45. A method of producing a filtration medium comprising: providing (1) a pollutant absorbent layer comprising a mat comprising a plurality of activated carbon fibers, and further comprising metal halide salts, metal hydroxides, inorganic acids, or combinations thereof, or (2) a pollutant absorbent layer comprising a mat comprising a plurality of activated carbon fibers treated with a mercury retention species; positioning a non-woven fiber glass fabric adjacent to a first surface of the pollutant absorbent layer; positioning a woven fiber glass fabric adjacent to a second surface of the pollutant absorbent layer; and needling the non-woven fiber glass fabric and the woven fiber glass fabric to the pollutant absorbent layer.
 46. The method of claim 45, further comprising: positioning a second non-woven fabric adjacent to the woven fabric prior to needling.
 47. The method of claim 45, further comprising applying a coating to at least one of a fluid inlet surface or a fluid outlet surface of the filtration medium.
 48. The method of claim 45, further comprising attaching a membrane to a fluid inlet surface of the filtration medium.
 49. The method of claim 48, wherein the fluorocarbon comprises polytetrafluoroethylene.
 50. The method of claim 45, wherein the pollutant absorbent layer comprises a metal halide salt.
 51. The method of claim 50, wherein the metal halide salt comprises zinc chloride, zinc bromide, potassium chloride, potassium bromide, potassium iodide, or combinations thereof. 